Bob Greene, Oprah's fitness expert and friend, has been with her every step of the way during her weight loss ups and downs. After joining the intense Boot Camp, Oprah "got with the program" and made a commitment to her health.

During a trip to Africa, Oprah strayed from Bob's healthy eating plan. She admits that she ate bread and potatoes almost every night—and now she's paying for it! When she returned from her vacation a few pounds heavier, Oprah says Bob asked her, "Has anybody told you the truth about yourself?"

The truth is, Bob says, most people need a wake-up call. For some people—like Oprah—you need to be a little bit tough. Oprah admits that she probably wouldn't have listened to anything Bob taught her if he had said it nicely. "I need that sledgehammer," she says.

Weight loss is a daily struggle for many people—including Oprah. Bob says every dieter should keep in mind two sets of weight loss rules. "There's one set for just making the scale move," he says. "That just follows the laws of physics—you have to do x, y and z, and if you do them, the scale moves. But then there's the other thing...what's going to keep you doing those things for the rest of your life? That's where it gets complicated."